南苏丹Melut盆地北部坳陷烃源岩热演化特征及油气地质意义

Thermal evolution characteristics of source rocks and their petroleum geological significance in the Northern depression of Melut Basin, South Sudan

南苏丹Melut盆地烃源岩热演化特征研究对盆地油气勘探具有指导意义。通过地质、地球化学资料分析及含油气系统模拟技术,在恢复北部坳陷热史基础上,利用"Easy%Ro"动力学模拟方法模拟计算了Renk组烃源岩的成熟史,同时利用"Ro—排烃率"模型对Renk组的生排烃史进行了研究。结果表明,北部坳陷的3个凹陷Renk组烃源岩热演化程度存在一定差异,Jamous凹陷进入成熟、高成熟、过成熟的时间最早,Ruman凹陷次之,Moleeta凹陷最晚。由于热演化史的差异,导致北部坳陷的3个凹陷在生排烃时间上也具有一定差异性,Jamous凹陷在白垩世晚期(88Ma)开始排烃,在古新世进入大规模排烃阶段,而Ruman凹陷及Moleeta凹陷进入大规模排烃阶段的时间在始新世。整体而言,北部坳陷烃源岩生排烃时间与Yabus/Samma组、Galhak组与Gayger组圈闭、盖层形成时间有良好的匹配关系,影响Yabus/Samma组成藏的主控因素是油源断裂,而Gayger组与Galhak组成藏的主控因素是储层物性。同时热演化程度高、持续排烃的Renk组烃源岩为北部坳陷地层—岩性油藏的油气充注提供了丰富的物质基础。因此,地层—岩性油藏应为北部坳陷重要的勘探接替领域,值得进一步研究探索。

The study on thermal evolution characteristics of source rocks in the Melut Basin in South Sudan is of great significance for oil and gas exploration in the basin. Through the comprehensive analysis of geological and geochemical data, and petroleum system modeling, the maturity history of the source rocks in the Renk Formation was simulated by "Easy% Ro" dynamic simulation method on the basis of restoration of the thermal history of the Northern depression. Meanwhile, the "Ro– hydrocarbon expulsion rate" model was used to study the hydrocarbon generation and expulsion history of source rock in the Renk Formation. The results show that there are some differences in the thermal evolution degree of source rocks in the Renk Formation of the three sags in the Northern depression. The source rocks in the Jamous sag was the earliest entering the stages of mature, high mature and over mature, followed by those in the Ruman sag. Source rocks in the Moleeta sag was the latest. Due to the difference of thermal evolution history, there are some differences in hydrocarbon generation and expulsion time among the three sags in the Northern depression. Source rocks in the Jamous sag began to expel hydrocarbon in the late Cretaceous(88 Ma), and entered the large-scale hydrocarbon expulsion stage in the Paleocene. While the large-scale hydrocarbon expulsion period of source rocks in the Ruman sag and the Moleeta sag was in Eocene. Overall, the hydrocarbon generation and expulsion times of source rocks in the Northern depression are of good matching relationship with the formation times of traps and cap rocks of the Yabus/Samma Formation, Galhak Formation and Gayger Formation. The main controlling factor of hydrocarbon accumulation in the Yabus Samma Formation is oil-migration fault, while that in the Gayger Formation and Galhak Formation is reservoir physical properties. At the same time, the source rocks in the Renk Formation were of high thermal evolution and continuously expelling hydrocarbon, which provided rich material basis for oil and gas charging into the stratigraphic-lithologic reservoirs in the Northern depression. Therefore, stratigraphic-lithologic reservoirs should be an important exploration field for future in the Northern depression, which is worth further research and exploration.